KR20040111460A - Data channel procedure for systems employing frequency diversity - Google Patents

Abstract

The present invention relates to a method for facilitating bidirectional data transfer between devices using frequency diversity for use in wireless data communication. This is generally suitable for units that achieve frequency diversity by frequency hopped spread spectrum operation. The basic unit of the present invention is an individual data frame whose reliability is improved by a unique combination of redundant error correction coding, time diversity and frequency diversity. The present invention also extends the concept of individual data frames to complete an asynchronous data message that includes both call establishment and traffic phases. The traffic phase extends the begon data frames to include complete data messages. A message that already contains enhancements to the underlying data frame is also enhanced by repeating itself as many times as possible to embed it in transmission. To allow asynchronous operation, the call establishment phase is transmitted using a known frequency sequence, the traffic phase is pseudo-randomly ordered in such a way that the entire transmission appears pseudo-random and all frequencies are used equally on average.

Description

Data channel procedure for systems employing frequency diversity

The wireless industry has grown tremendously over the past few years. Wireless communication has become a common part of everyday life. Most people find that in various aspects of their daily lives, Global System for Mobile Communication (GSM), Universal Mobile Telecommunications System (UMTS), Carrier Detection Multiple Access (CDMA) And several different forms of wireless communication such as 802.11.

In general, wireless systems are designed for a specific area of footprint or coverage. These regions are generally called cells. Cells enable reuse of similar frequencies by multiple sources to support services in metropolitan areas that are somewhat distant. The geographic size of the cells does not need to be consistent over a given area, but may change due to frequency and power levels, the topography of that area, time of day, and the like. Communication within these cells takes advantage of the concept known as Demand Assigned Multiple Access (DAMA). DAMA allows multiple devices to access the network in a shared manner based on demand. Basically, devices access the network based on first-come, first-served processing. Within a wireless network, there are various ways in which multiple access can be provided to end users. At the most basic level, there is a Frequency Division Multiple Access (FDMA) methodology, which is essentially the starting point for all wireless communications, each of which must be separated by frequencies to avoid interference between wireless devices. The cell is given.

Another communication methodology that is relatively new and has its origin in spread spectrum radios is known as Code Division Multiple Access (CDMA). Spread spectrum radio is spread over the bandwidth of signals transmitted over a spectrum of radio frequencies. The combined spectrum of radio frequencies is generally much broader than necessary to support narrowband transmission of the signal. The spread spectrum uses two techniques, direct sequence (DS) and frequency hopping (FH). In short, DS spread spectrum is a packet radio technology in which narrowband signals are spread over a wide range of carrier frequency bands. In other words, signal information is organized into packets, each of which is transmitted over a wide range of carrier band frequencies in a redundant manner, i.e., in which packets are transmitted one or more times. Multiple transmissions can be supported. Transmissions from specific terminals are identified by a unique code, such as a 10-bit code that is pre-pended in each data packet. Most new technologies, such as CDMA, 802.11, and wireless applications, use the Direct Sequence Spread Spectrum (DSSS). However, Bluetooth and the present invention use Frequency Hopping Spread Spectrum (FHSS). In some cases, 802.11 uses FH mode. FHSS involves the transmission of short bursts of packets in a broadband carrier over a range of frequencies. In essence, the transmitter and receiver hop from one frequency to another in an organized hop sequence, with multiple packets being transmitted at each frequency. The hop sequence is controlled by a centralized base station antenna in the case of a land mobile trunked system such as cellular. When a cellular system is not available due to lack of coverage within a given area or busy cells, an alternative mode of communication may be needed. This mode is often referred to as "talk-around" or "direct mode" and allows two wireless devices to communicate directly with each other, similar to common two-way radios. Embodiments of the present invention relate to this talk-around mode of operation.

When operating at 900 MHz and 2.4 GHz unlicensed but regulated Federal Communications Commission (FCC) bands at high power, interference with other users of the same band must be avoided. For example, the 900 MHz band is used by cordless phones and the 2.4 GHz Industrial Scientific and Medical band (ISM) is used by IEEE 802.11 or Bluetooth compliant wireless devices. Inherent non interferer can be achieved by using spread spectrum, which includes the DS technique and the FH technique, as described above.

For many reasons, the scope of voice information transmission using FH is somewhat limited. For data features, there is a need to handle functions and applications such as text messages and multiplayer games and GPS location information. Moreover, since the range of data transmission can be designed to exceed the voice range, it is possible to send text messages when the voice functions can no longer operate. For example, in the case of a cell phone or other voice personal communication device, the receiving unit may receive at least the caller identity even if no voice call is heard. Thus, at a minimum, the user can identify a third party who attempted to make a contact.

There is a need for the availability of systems and methods to provide reliable transmission of blocks. For example, private identification of the originating mobile device must be transmitted reliably. In attempts to achieve reliable transmission of personal identification, certain problems arise with insufficient detection of signal detection, transmission message lengths, communication ranges and frequencies of the frequency hopping set. These shortcomings relate to data communication restrictions, along with requirements that meet the guidelines for the FCC addressed in US 47CFR 15.247-15.249, as well as similar regulations in other countries. As such, a need exists for a system and method for handling the use of frequency hopping for data channels. There is also a need to provide performance gain and reliability in the transmission of data.

The present invention relates to wireless system communication. In particular, the present invention relates to a data channel procedure that facilitates communication transfer between digital devices using frequency hopping.

1A is a block diagram of an exemplary wireless communication system in which the present invention may be practiced.

1B is a block diagram illustrating remote units communicating directly in talk-around mode outside of the network.

2 is an electrical block diagram of an exemplary remote unit in accordance with the present invention.

3 is a block diagram of an exemplary digital channel procedure for implementing a fundamental frequency hopped data frame.

4A shows frames of a complete data transfer protocol padded with zeros, without repetition of the message.

4B illustrates an improved scenario of the present invention illustrating frames in a digital channel procedure transmission signal that are padded with zeros with repetitions of the entire message.

The present invention relates to systems and methods for use in wireless system communications. In particular, the present invention relates to facilitating data communication between digital devices using frequency hopping spread spectrum coding.

The key to the present invention is the development of frequency-hopped data frames that reliably transmit a single data unit that is suitable for the minimum data size required by a given application. For example, such data unit may be an identification number of the device. Reliability and performance gains are realized by applying forward error correction and iterative diversity. Moreover, by repeating the coded and repeated data on multiple frequencies, the additional benefit of frequency diversity is achieved, as required for frequency hopping (FH) systems. Frequency diversity provides gain by interference avoidance and uncorrected channel fading. This basic data frame can be used to insert data (such as a device identifier) into other applications, such as digital FH voice transmissions. In another aspect of the present invention, a basic data frame may be associated with others to provide a complete data transfer protocol between FH devices. The method of the present invention utilizes a pseudo pseudo random generator to provide offline operations outside the fixed network infrastructure, de-emphasize the selection of known call setup frequencies in the transport packet, and Randomly ordered frequencies are used to transmit data traffic packets, thus realizing frequency diversity. The method applies two or more FH devices that communicate directly with each other without communicating over a network, such as digital bidirectional data / voice radios, for example.

The present invention provides a unique system and method for data processing and transmission between remote mobile units. The present invention can be applied to wireless system communication. In particular, the present invention relates to facilitating communication between digital devices using spread spectrum coding for transmission of data.

1, a block diagram illustrates a wireless communication system in an environment in which the present invention may be practiced. It should be noted that the present invention may be practiced directly between devices that cannot operate in the illustrated system and will be described with reference to FIG. 1B. As shown in FIG. 1, the fixed portion 108 includes one or more base stations 106 that provide communication for a plurality of remote user devices 102. Base stations 106 coupled by communication link 116 preferably communicate with user device 102 using conventional radio frequency techniques. One or more antennas 104 provide the remote user device 102 from the base stations 106. In addition, the base stations 106 preferably also receive RF signals via the antenna 104 from the plurality of remote user device units 102.

The fixed portion 108 of the communication network 100 connects to a public switch telephone network (PSTN) for receiving and sending messages to other device types, such as telephone 112 and computer 114. do. Calls or information initiated or intended for the remote user device 102 may be received by or originated from a device such as the telephone 112 or the computer 114. Those skilled in the art recognize that alternative forms of networks, such as, for example, local area networks (LAN), remote networks (WAN), and the Internet, may be used to receive or transmit selective call information to the wireless network 100. . A computer, such as computer 114, may also serve as a central repository for various applications and information used by the wireless communication system.

It will also be appreciated that the present invention is applicable to other forms of wireless communication systems, including dispatch systems, cellular telephone systems, and voice and / or data messaging systems.

1B shows an alternative communication mode of talk-around. In talk-around mode, two or more remote user devices 102 communicate directly with each other outside of the network. The present invention provides certain advantages for non-network communications between user device 102. In particular, an embodiment of the present application provides direct communication to a remote device such as digital walkie-talkies that are not associated with any network. An exemplary remote user device 102 that may be used with the present invention will be discussed with reference to FIG.

2 illustrates an example remote user device 102 and various components. The remote user device 102 includes an antenna 202 that is used to receive inbound messages and send outbound messages. Antenna 202 is coupled to transmitter 204 and receiver 206. Both transmitter 204 and receiver 206 are connected to processor 216 to process information regarding outbound and inbound messages and to control remote user device 102 in accordance with the present invention. User interface 210 is operatively connected to processor 216 to provide user interaction and feedback. In an embodiment of the invention, the user interface 210 includes a display 212 and a keyboard 214. Display 212 provides the user with effective information and feedback from processor 216. The keyboard 214 allows a user to provide input or response to the processor 216. Other methods and systems for user interaction and feedback can also be used to achieve the objects of the present invention. The crystal oscillator 208 provides conventional timing to the processor 216 and other components of the remote user device 102. Processing is performed by processor 216 along with memory 218. Memory 218 includes software instructions and data for programming and operating remote user device 102 in accordance with the present invention. Remote user device 102 operates to communicate with base station 106 or other remote user device 102. In order to be able to identify the caller even when no voice is heard, it is necessary to transmit blocks of data with high reliability regardless of the target.

Reliable transmission of data will be discussed with reference to FIG. 3. In particular, in embodiments of the present invention, reliable transmission of basic units of data, such as personal identification of originating mobile devices, will be discussed. However, one skilled in the art will recognize that the system and method of the present invention may equally apply to other data items, such as text messages. In general, data associated with the identification of a mobile user device should be able to receive at very low Signal-to-Noise Ratios (SNRs). In other words, there must be some form of communication that can occur when the SNR is not high enough for good sound quality. If the other party cannot easily hear the caller during the digital voice operation, the called person should at least know the calling person. Moreover, users can also choose to communicate using short text messages when voice communication is not possible, and the transmission of such messages becomes more reliable by the present invention.

In order to achieve the purpose of reliable transmission, a data channel procedure (DCP) with overhead applied to the data information signal is implemented. Mechanisms used in this process may include one or more forward error-correction (FEC), iterative diversity and cyclic redundancy check (CRC) codes.

3 shows a DCP designed for systems for achieving frequency diversity for transmission signals. In an embodiment of the present invention, the modulation scheme used is 3200 symbols per second and is an orthogonal frequency shifting scheme (8-FSK) using non-coherent detection. The symbol is derived from the modulation coding of the bits of the transmitted data. In the illustrated embodiment 300, an operating frequency is used in the ISM band of 902-928 MHz with a frequency hopping carrier spacing of 50 KHz. Each hop-set consists of 50 carriers and each of these frequencies must be used evenly due to FCC adjustments.

In the exemplary DCP 300, a 34-bit block of data √ is transmitted at step 302. This data may be the originator's PID, a text message or some other data. To help explain the present invention, various indicia and symbols are used in this description. E.g, A vector denoted by means a vector of bits, and a vector denoted by “▶” denotes a vector of 8-FSK symbols. Subscripts to the vectors are also provided to represent the functions performed on the vector. For example, the subscript 'S' indicates data bits of the associated vector with added Stop Bits, 'C' indicates that a CRC has been performed, 'F' indicates that flush bits have been added, R 'indicates that one or more iterations have been performed.

Returning to exemplary DCP 300, in step 304 a stop bit is added to the 34 bits of data √, resulting in 35 bits of data √ _S. Following this, the 12-bit CRC generator in step 306 yields the 47-bit block √ _SC :

is performed using g (x) = 1 + x + x ² + x ³ + x ¹¹ + x ¹²

Since a conventional encoder with four memory elements is used, four flush bits of zeros need to be added to enable the conventional encoder to exit in a known state. Four flush bits are added in step 308 to the 47-bit block √ _SC to provide a 51 length block √ _SCF . In step 310, block √ _SCF passes at a conventional encoder 1/3 speed. The encoder essentially converts the bits into symbols using 8-FSK mapping. In the example DCP 300, although mapped to 3 bits per symbol, however, 1/3 coding also occurs, so each bit is eventually represented as a symbol after 8-FSK mapping, thus 51 symbols ▶ causes.

The next requirement in DCP is the need for time diversity that allows multiple instances of the message block to be created. To generate time diversity, the 51 symbols of step 310 are repeated five times in step 312 to yield 255 symbols _{R R.} One symbol is added on it to produce a 256 symbol length ▶ _RS in step 314. In step 316 an interleaver 8 x 32 block is used to obtain 256 length vectors, _RSI . An 8 x 32 time interleave block provides scrambling of symbols and helps to overcome de-correlation, fading and other similar problems. In essence, time interleaving scrambles the message by reordering the signals. The next step is the application of frequency diversity.

Frequency diversity may provide a distinction between repeated blocks while improving the chances of successful transmission of the message block. To produce frequency diversity, the 256 length vector _RSI can be repeated for any number of bursts. Number N of bursts with repeated _RSI is flexible. Each iteration provides diversity gain and thus improves performance. While each iteration also slows the supported data rate, this slowness is actually necessary to achieve the desired range and performance. In an embodiment of the invention, three N values are selected in step 318. This N burst frame produces a basic data unit. In FH systems, frequency diversity is achieved because each burst is for a different frequency. This data unit can be inserted into other FH streams, such as voice.

The next aspect of the present invention is the extension of basic data units to a complete data transfer protocol. Details of this compliance process will be described with reference to FIG. 4A.

In certain applications, the sending of short messages results in certain problems resulting from the requirements of FCC adjustments. In particular, there is a need for equal distribution and use of all frequencies in the spread spectrum. Each hop-set in specific applications of the 900 MHz ISM band includes 50 frequencies and channels. It is required by FCC rules for transmission to use each of the 50 frequencies at least equally. In order to synchronize the mobile devices in a manner that does not exceed the drain power, six (6) of the 50 frequencies in the hop-set are transmitted at the beginning of the transmission to achieve call setup. Referring to FIG. 4A, the frequencies are transmitted in a fixed pattern as a preamble 402 and a sync 404. During voice or data traffic, the selection of these fixed pattern frequencies is de-emphasized by a pseudo random generator such that the overall frequency distribution remains even. For example, in voice transmission, there are six frequencies that are de-emphasized throughout most of the transmission, with all frequencies being used evenly. Long transmissions are actually crucial for unbalancing frequency usage. However, with the data the message can be shortened, so the transmission is short. This limits the power of unbalanced frequency use. A solution is provided through the padding and / or repetition of the data message in such a way that a fixed transmission length is implemented.

Using short messages, such as text, there is a good chance that conventional messages are seriously out of balance of frequency usage. For example, consider messages of twenty characters that are typical character lengths. As previously described, each DCP frame can have 4.25 characters. Thus, twenty character messages require five DCP frames. The DCP frame is transmitted on three hops, so these five DCP frames will need fifteen frequency hops. For synchronization purposes, a typical message uses 50 frequencies in the hop-set. This suggests that the use of 50 frequencies cannot be balanced.

In general, in an effort to balance frequency distribution, during the traffic portion of the transmission, among the frequencies used to transmit the message, it is de-emphasized by a pseudo random generator of choice for six preambles and synchronization frequencies. It is unlikely to be chosen as one. In other words, each of the preambles and syncs used for the message only six of the fifty frequencies will be transmitted exactly once. The remaining 44 frequencies from the messages are transmitted on average 15/44 = 0.34 times, respectively, without such de-emphasis. Thus, any opportunities to balance frequencies are eliminated.

This problem of frequency balancing is addressed by the present invention illustrated and described with reference to FIG. 4A. As shown, any message extends to 19 DCP frames regardless of the actual message length. In other words, each message lies on 57 frequencies (19 DCP * 3 frequency hops per DCP). In fact, each message is extended to messages of 4.25 * 19 = 80.75 characters. The preamble 402 of the three frequencies and also the synchronization 404 of the three frequencies are de-emphasized during the selection, during the traffic. At traffic frequencies, there is a lower probability of being selected than the remaining 44 frequencies of a typical 50 frequency message. The amount of de-emphasis can be seen by looking at the average number of frequencies used. The probability of selecting a frequency by a pseudo random generator during traffic to send a message can be expressed as follows:

During transmission, for all 63 bursts in the modified message, there are 57 traffic bursts in addition to six preambles and sync bursts. With the weights represented by the above equation for traffic frequencies, each of the 50 channels in the hop-set will be used. The average use would be 63/50 = 1.26 times, which is a balanced frequency use.

For sufficiently short messages, it is advantageous to use a point that requires padding for additional message repetition, as opposed to simply padding with zeros, as shown in FIG. 4B. When the message is repeated, the CRC on each DCP frame can be used to determine if the iteration is decoded correctly. The transmit signal 410 of FIG. 4B includes three burst preambles 402, three burst syncs 404, equally repeating text message blocks 406, 410, 412 and padding 414. As shown, 19 DCP frames of the signal are used to repeat the text message as many times as possible with zero padding at the end.

As mentioned above, in the embodiment of the present invention the number of bursts for the selected data iterations is three. As such, message 406 repeats with messages 410 and 412. This DCP implementation of the present invention allows the transmission of blocks of message data to have high reliability.

The advantages of the DCP of the present invention are also illustrated by the results of the exemplary simulation. The simulation environment was a Rayleigh fading channel using a mobile unit speed of 3 MPH. Fading for each of the frequency hops was taken independently. The receiver used a bank of matched filters, one for each of the eight FSK frequencies, to generate a set of eight composite statistics for each symbol interval. The sets of statistics corresponding to repeated symbols on hops and on different hops were squared combined.

The combined statistics of these symbols were input to the Viterbi decoder. The decoder used a squared combination of branch metrics to form path metrics.

In the above-described environment, the following results were obtained for the reception of the personal identification (PID) of the originating mobile device. One of the guidelines in the simulation was that if any bits of the PID failed, the entire PID would be rejected. For a very low E _S / N ₀ of 3 dB, where E _S represents symbol energy and N ₀ represents noise spectral density, it was observed that the PID received 99% of the time. At 6dB, the PID received more than 99.9% of the time. To further illustrate the advantages and operations of the present invention, the transmission message of varying character lengths is evaluated in the simulation environment described previously, using the inventive DCP design.

In particular, for messages of 17, 34, 51 and 68 character lengths, consider the probability that the entire message will not be decoded correctly. The value of E _S / N ₀ in which the entire message is received more than 99% correctly then will be used as a metric here.

The above-described embodiment of the present invention uses 19 DCP frames for the transmission of a message with 4.25 characters per DCP. As such, nineteen-character messages requiring four DCPs (17 / 4.25) will be sent four times within the DCP message length of nineteen. 17-character message requires a lot of values below the point at which correctly received the preamble and sync, about -1dB the E _S / N _0. The 34-character message will be sent twice and requires about 2 dB of E _S / N ₀ , with preamble and sync still below the levels that are reliably received. In general, the large function of text messages is within this range of 34 characters with an SNR of 2 dB.

Longer 51 and 68 character messages are sent only once for a length of 19 DCP messages. These require E _S / N ₀ values between 6 dB and 7 dB, which is near the point where the preamble and synchronization have been reliably received. Even at 4 dB E _S / N ₀ , the message is decoded more than 90% of the time.

From the results, it is further argued that the messages with which the limiting factor of the text message at the very low values of E _S / N ₀ become preamble and detection of synchronization are sufficiently high and decoded with very high confidence.

The present invention has been described with respect to specific embodiments which are intended to be illustrative rather than restrictive in all respects. Alternative embodiments will be apparent to those skilled in the art without departing from the scope of the present invention.

From the foregoing, it will be appreciated that the present invention is adapted to attain all of the objects and objectives described above, together with other obvious and inherent advantages to the system and method. It will be appreciated that certain parts and subcombinations may be used and may be used without reference to other parts and subcombinations. This is expected and within the scope of the claims.

Claims (10)

A method of using wireless communication to facilitate bidirectional data transfer between devices using frequency diversity, the method comprising: Providing a basic data frame with a bit length sufficient to convey a minimum amount of information for a given application; Encoding the elementary data frame through redundant forward error-correction coding; Repeating the encoded data to provide time diversity; And further repeating the encoded data on multiple frequencies to provide frequency diversity and improve frequency hobbed spread spectrum capability. The method of claim 1, And said encoding step of said basic data frame through forward error correction coding improves performance and reliability. The method of claim 1, And said iterating said encoded data for time diversity further improves performance. The method of claim 1, Packaging the base data frame for application in non-data frequency hobbed applications. A method for wireless communication of a data message, comprising: Providing multiple basic data frames for encompassing the data message; Fitting as many copies of the data message as possible within the entire transmission; Padding the remainder of the entire transmission with a value to achieve a uniform transmission length. The method of claim 5, wherein And the value used for the padding is zero. A method for asynchronous wireless communication of data between devices using frequency hopped spread spectrum operation, the method comprising: A call-build step using a known frequency sequence, Traffic stages, A pseudo random sequence generator for providing a selection of said known frequency sequence, Wherein said selection by said pseudo random sequence generator de-emphasizes said known frequency sequence during said traffic phase, such that all selected known frequencies are equally used on average. A method of using wireless communications to transmit data, the method comprising: Extending the traffic portion of the data transmission message to a transmission signal length that enables balanced use of a plurality of frequencies; De-emphasizing the selection of the initial subset of the plurality of frequencies during data traffic; Multiple iterations of short messages at remaining frequencies within the transmission signal length. The method of claim 8, De-emphasizing the selection of the initial subset of the plurality of frequencies is accomplished by using a pseudo random generator. The method of claim 8, And said initial subset of said plurality of frequencies is represented within a first portion of said transmission signal length and comprises uniform control signals such as preambles and synchronization bursts.